You can't beat perfect. I've run the regular plugs for the last 10 years and my bikes run perfect all the time. Why spend more. Repeat after me. Perfect.

very well said. I have to agree. This is my first Harley, but with all the Japanese bikes I've owed over the past decades, a version of the same goes. Put the correct NGK plug in and ride it like you stole it. They run "Perfect" like that.

Just because the box states its preset to .035 doesn't mean they actually are. I very rarely get a set of plugs that are in their pre-gapped state. So double check with a good gapping tool before install.

If your talking about a diff in performance depending on the gap, I don't see how. If your talking about a diff in performance based on indexing, I also don't see how. Both are controlled by the laws of physics.

You won't see a performance difference with SE plugs over standard. Only difference will be in your wallet. I've used Autolite spark plugs in my bike for over 50k miles without issues. A lot cheaper, and better quality then HD's.

I seriously doubt a 60 mile difference in milage was caused by changing your spark plugs. That would be a 50% improvement. Or 24 mpg before the SE plugs and 36 mpg with the SE plugs (with a 5 gallon tank). More then likely your old plugs were just shot or you aren't drag racing from stop light to stop light as much anymore. Just sayin'...

Call it what you will my wallet disagree's with you period it is what it is. My last plugs had 4000 miles on them. And I don't drag race anywhere.

The reason the plugs are gapped to a certain spec is because the heat range for optimum performance for that motor set up. That could be the reason your not getting the mileage.

I was the engine builder for a camel pro flat track racer and you might be surprised what kind of work goes into spark plug correctness if you will. IT DOES MAKE A DIFFERENCE.

I am changing screaming eagle plugs on my hi compression motor. (#32186-10). I was told to gap them @ 040. however the box stated they were preset @ 035 for that particular part number, Other than the difference of 005, what would be the difference performance wise?

This could be an interesting thread, kind of like the oil threads, to see what reasons people have for making the decisions they do.

I have a couple of curious questions.

WHO told you to gap them at 040? Is it someone whose advice you trust?

For plugs that come preset at a particular gap, does that mean they are intended to always stay at that gap or is that just a "default setting"?

__________________G Man

Meddle not in the affairs of dragons for you are crunchy and taste good with ketchup.

This could be an interesting thread, kind of like the oil threads, to see what reasons people have for making the decisions they do.

I have a couple of curious questions.

WHO told you to gap them at 040? Is it someone whose advice you trust?

For plugs that come preset at a particular gap, does that mean they are intended to always stay at that gap or is that just a "default setting"?

G MAN pretty sure it is a default setting. Even if your motor is suppose to be set at .035 and the box of the new plug says .035 gaped from the factory its still a good idea to double check them.

The wider the gap the more "force" the coil has to put out to "close" the gap. The smaller the gap the coil doesn't have to work as hard. Also this would be for stock coils.

Now the 64 thousand dollar question is "will the other plugs work?" Of course they will and as stated before perfect. I just choose the SE plugs. Yes they do cost more but I'm willing to pay the extra. Just MY personal choice.

My opinion is that your wasting money on the name for these plugs. Im sure the Mothership gets them from another brand company. I have used NGK and others with the platinum or irridium centers and have had no issues....they burn well, last a long time

I am changing screaming eagle plugs on my hi compression motor. (#32186-10). I was told to gap them @ 040. however the box stated they were preset @ 035 for that particular part number, Other than the difference of 005, what would be the difference performance wise?

Quote:

Originally Posted by rayo1

how critical is indexing when installing plugs. is performance affected.

Due to my own ignorance, I did a little research about this stuff and found:

As a rule of thumb, higher compression engines may want a larger gap. Smaller gaps can lead to preignition. Too large of a gap can lead to mis-firing. I would guess the reason would be that the larger the gap, the more charge must build up to jump the gap (i.e. fires slightly later) but if the gap gets too big, the spark may not jump. Likewise, upgrading the ignition to higher output will allow the spark to jump the larger gap. So this is why a higher compression engine should include a higher output ignition system.

As far as performance, indexing will produce a negligible difference in an engine that produces less than 200 HP. To even get the slight, unnoticeable gain you would need to do quite a bit of dyno testing and experimenting to determine where to index to (pointing toward intake or exhaust valve) since the results can vary between different engines.

It seems the main benefit of the SE plugs is due to the fine core electrode and V ground. The theory is that there is less restriction to the flame front and less buildup of carbon allowed due to the decreased surface area. This would theoretically increase the life of the plug and discourage fouling. Is it enough to justify the cost?

Nightrider's web site has some good info on this subject.

I think the answers to your questions may be that you want to stay closer to the .040 gap with your high compression engine and don't expect any real performance gains by using SE plugs or by indexing. The SE might give you a longer usable life on the plugs.

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